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Evolution of Strategic Flood Risk Management in Support of Social Justice, Ecosystem Health, and Resilience

Summary and Keywords

Throughout history, flood management practice has evolved in response to flood events. This heuristic approach has yielded some important incremental shifts in both policy and planning (from the need to plan at a catchment scale to the recognition that flooding arises from multiple sources and that defenses, no matter how reliable, fail). Progress, however, has been painfully slow and sporadic, but a new, more strategic, approach is now emerging.

A strategic approach does not, however, simply sustain an acceptable level of flood defence. Strategic Flood Risk Management (SFRM) is an approach that relies upon an adaptable portfolio of measures and policies to deliver outcomes that are socially just (when assessed against egalitarian, utilitarian, and Rawlsian principles), contribute positively to ecosystem services, and promote resilience. In doing so, SFRM offers a practical policy and planning framework to transform our understanding of risk and move toward a flood-resilient society. A strategic approach to flood management involves much more than simply reducing the chance of damage through the provision of “strong” structures and recognizes adaptive management as much more than simply “wait and see.” SFRM is inherently risk based and implemented through a continuous process of review and adaptation that seeks to actively manage future uncertainty, a characteristic that sets it apart from the linear flood defense planning paradigm based upon a more certain view of the future.

In doing so, SFRM accepts there is no silver bullet to flood issues and that people and economies cannot always be protected from flooding. It accepts flooding as an important ecosystem function and that a legitimate ecosystem service is its contribution to flood risk management. Perhaps most importantly, however, SFRM enables the inherent conflicts as well as opportunities that characterize flood management choices to be openly debated, priorities to be set, and difficult investment choices to be made.

Modern flood risk management has emerged over the past decades in response to lessons learned from flood events and advances in science and engineering. This process of change continues at an accelerated pace as the need for a more strategic approach is increasingly recognized. Such an approach recognizes that there is seldom a single solution to managing flood challenges and promotes the use of a portfolio of flood risk management measures and instruments (Evans et al., 2004a, 2004b; Klijn, de Bruijn, Knoop, & Kwadijk, 2012; Klijn, van Buuren, & van Rooij, 2004; Sayers et al., 2014; van Herk, Zevenbergen, Gersonius, Waals, & Kelder, 2014). The U.K. Climate Change Risk Assessment reinforced the need for such an approach and calls for an Enhanced Whole System approach to flood risk management (Sayers, Horritt, Penning-Rowsell, & Mckenzie, 2015a; Sayers, Horritt, Penning-Rowsell, Mckenzie, & Thompson, 2016a) that brings together actions to manage the probability of flooding (such as traditional defenses, but also natural flood management measures), to reduce exposure to flooding when it occurs (through better spatial planning), and to reduce the vulnerability of those that may be exposed (by improving flood forecasts and warnings as well as policy instruments such as insurance and homeowner grants for flood proofing).

There is also a recognition that the criteria for assessing flood risk management activities should involve consideration of a much broader set of outcomes than the traditional focus on easily defined national economic impacts. This includes the contribution to social justice (e.g., Johnson, Penning-Rowsell, & Parker, 2007; Sayers, Horritt, Penning-Rowsell, & Knox, 2016b), ecosystem services (e.g., Environment Agency, 2014; SEPA, 2012; WWF, 2011), and local economic opportunities (e.g., Pike et al., 2016). Equally, an increasing recognition of non-stationarity within the flood system (climate, geomorphologic, and socio-economic change) forces an explicit consideration of a full range of plausible ways in which flood risk may shift in the future. This continuous process of adaptation is distinct from the “implement and maintain” philosophy of a traditional flood defense approach.

This article sets out some of the most influential flood events that have driven these changes and some of the remaining issues and challenges. The emerging approach of strategic flood risk management (SFRM) is discussed in the context of these challenges together with the principles that guide its implementation in practice.

Flood Management: A Historical Perspective

The earliest civilizations recognized the need to live alongside floods: locating critical infrastructure on the highest land (as seen through the churches and cathedrals of England (Murphy, 2009) and the historic settlements built on artificial earth mounds, known as “terps” within the floodplains of the Netherlands, Denmark, and Germany (Snyder, 2010); providing flood warnings to those that may be flooded (common practice in ancient Egypt; Gulhati & Smith, 1967); and making flood-sensitive land use planning choices (as often practiced by the Romans).

As populations grew and people began to gather together into larger villages, towns, and cities, there was a need to increase agricultural production. Floodplains became more crowded with crops and permanent settlements. The periodic intrusion of flood waters became less acceptable. What was once seen to be an inconvenience became a challenge to societies. This changing relationship is highlighted by the scholar Saxo Grammaticus within his works on the history of Denmark to 1185 that remarks upon the cultivation of coastal marshes of southwestern Jutland “whether this is perhaps a case of buying gold too dear. Because, it is a risky affair with that coast. When a violent storm comes about, it may well happen that the sea breaks the dikes that are built for protection, and intrudes so fiercely that not only the standing crop is flushed away, but also the houses together with the people and whatever” (Gesta Danorum, “Deeds of the Danes”; Davidson & Fischer, 1979apud Sayers et al., 2014, p. 32).

As far back as 4600 bce, Chinese engineers, faced with similar development pressures, constructed dikes in an attempt to control flooding (Qingzhou, 2002). When around 2500 bce a series of severe floods within the Yellow River breached poorly constructed dikes, mythology and fact combine to suggest that Emperor Yu (2205 bce) began to recognize system connectivity and constructed nine separate diversion channels (lined with dikes through settled areas) to convey the flood waters of the Yellow River to other rivers and out to the sea. Between 403 and 221 bce the construction of further major control structures took place, including the Dujiang Weir, Zhengguo Canal, and Hong Ditch. During the Western Han Dynasty (206 bce–24 ce) development pressure continued to grow and the engineering proposals became increasingly elaborate to manage increasingly large and complex flood systems with decreasing success. In response, Jia Rang, a Chinese government official, published a new approach to flood management based on the philosophy “Do not fight against water for land” (Huang, 2014), where he proposed that space should be retained to “retard” flood flows and divert flood waters to less developed areas and farmland. He also suggested that levee construction should be a last resort. Although his advice largely went unheeded and the focus largely remained on dike construction, the concept of setting back secondary dikes to create storage capacity when the river was in flood was promoted (an early example of making room for the river).

Despite the warnings set forth in Gesta Danorum and the wisdom of Jia Rang, the requirement for protection and a belief in our ability to control floods started to increasingly dominate attempts to “deal with flooding.” Throughout the early and mid-decades of the 20th century, engineers sought to control flood flows and defend areas from flooding. Typically, this was accomplished via the construction of extensive levee systems and ring dikes, diversion channels, dams, and related structures. The perceived safety of the defended floodplains attracted development (for example, in New Orleans, London, Shanghai). Ecosystems became increasingly starved of the sediments and space upon which they rely (for example, in the Mississippi, Yangtze, Thames, Rhine, Danube), which in turn has affected the ecosystems services they provide.

Despite the structural protection and the high price of the loss of ecosystem functions, flood losses continued to increase and the need for change became increasingly apparent. In response, through the latter part of the 20th century, flood management was recognized not only as an engineering pursuit but also as a social endeavor (Baana & Klijn, 2004; White, 1945). A new approach was needed, one that could not only identify the hazards and the consequences faced by society but also assess the relative significance of the risks faced, and the concepts of flood risk management (based upon a longer-term, system-wide perspective) started to emerge (e.g., Evans et al., 2004a, 2004b; Sayers, Hall, & Meadowcroft, 2002; Schanze, 2006; Samuels, Morris, Sayers, Creutin, Kortenhaus, & Klijn, 2010; White, 1960). In more recent years the concepts of risk management have continued to evolve, in particular adopting an adaptive approach to managing flood risks, which works with natural processes, contributes positively to ecosystem services, and forms part of integrated basin or coastal management (e.g., WMO, 2009; Sayers et al., 2014). This progression is reflected in Figure 1.

Figure 1. The evolution and development of flood management (Sayers et al., 2014).

Selected Flood Events that have Influenced the Evolution of Flood Management Practice

Flood management approaches have developed across the world and continue to evolve in response to flood events, shifting societal priorities and increasingly complex demands placed upon flood managers. A collaborative analysis of international practice highlights the specific influence major flood events have often had in forcing and shaping these changes (Sayers et al., 2011, 2013).

1917and1927Floods in the United States and1931Flood in China: Promoted Awareness of the Need for Basin Scale Coordination The 1917 floods caused the U.S. federal government to take a greater interest in the Mississippi River and the Sacramento River basins. It was recognized that existing, siloed, local governance structures were simply unable to deal with such major basin wide floods, and they sought federal fiscal support. In 1927, heavy storms across the Midwest led again to widespread floods across the lower Mississippi Valley that eventually breached a locally controlled levee system and displaced many thousands of people from their homes and lands for several months (Barry, 2007). It was labeled a national tragedy and brought about immediate attention from the national government. In 1928, by act of Congress, the U.S. federal government assumed responsibility for the construction and major maintenance of flood control structures in the lower Mississippi Valley. The “levees-only” policy was closely examined and deemed to be insufficient to deal with the challenge of major floods (Myers & White, 1993). A comprehensive plan for flood control was to include strengthening of the levees, improvement of the channel to provide for natural maintenance, cutoffs of river bends that were seen to be delaying the flow of waters to the Gulf of Mexico, floodways to serve as pressure relief valves during major events, and flood storage dams on the Mississippi River tributaries.

A major flood in China in 1931 is generally considered the deadliest natural disaster ever recorded. The number of human deaths has been estimated to be from 1 million to as many as 4 million. These widespread floods were experienced across the three major rivers: the Yellow, Yangtze, and Huai. The Yellow River flooded first between July and November 1931, killing 1–2 million people and leaving 80 million homeless. The worst period for the Yangtze was from July to August 1931 and affected 28.5 million people. The Yangtze along with the Huai River flood rendered Nanjing city, capital of China at the time, an island. The high water mark was reached on August 19 at Hankou with the level exceeding 53 ft (16 m) above normal. These devastating floods were the catalyst to a more organized response to flood management in China. For example, following the flood the Huai River Conservancy Commission, which was formed in 1929, was charged with immediately addressing the flood problems (GIWP, 2013). The lack of funding and support would, however, limit its effectiveness. China continued to experience severe floods during the 1930s, ’40s, and ’50s. As part of the early years of the People’s Republic of China, action was taken to improve the capacity of flood control and land drainage systems. The measures typically included river dredging, raising and reinforcing dikes, connecting polder areas, and building sluices. In some river sections reservoirs were constructed and flood storage and retention areas developed. Increasingly more scientific and technological methods were used to support the design of control and storage works, often achieving immediate, but not always lasting, success (GIWP, 2013).

Although limited in the context of a risk management approach, this was important progress in thinking that promoted the need for basin scale infrastructure and coordination of action.

1947and1953Flood Events in Europe: Promoted the Need for Clearer Roles and Responsibilities and Better Warning Systems In March 1947, river floods occurred across much of Europe. The flooding was triggered by the rapid thaw of deep snow lying on a frozen catchment after one of the coldest and snowiest winters on record. The thaw was triggered by the arrival of a succession of southwesterly depressions, each bringing significant additional rainfall. Nearly all the main rivers in the south, midlands, and the northeast of England were in flood with 30 out of 40 English counties impacted over a two-week period. Tens of thousands of people were temporarily displaced from their homes, and thousands of acres of crops lost (Barker, 1948). Shortly after the 1947 fluvial floods, Europe experienced devastating coastal floods in 1953 when a surge tide swept south through the North Sea, overtopping and breaching many defenses in England, the Netherlands, and Belgium. The storm was at its peak during the night, and with little or no warning an estimated 2,400 people lost their lives, including 58 people on Canvey Island (Pollard, 1978). The net effect of these floods was to emphasize the fragility of structural defenses; yet, as throughout history, the response was to increase the investment in levees, floodwalls, floodways, and other structures. The event did, however, highlight the dramatic inadequacies in early warning systems and initiated the United Kingdom’s national Storm Tide Warning Service (Johnson, Tunstall, & Penning-Rowsell, 2005), a service that continues today.

The 1953 flood also had a profound impact on perception of flood risk in both England and the Netherlands. The Delta Committee (Dantzig, 1956) in the Netherlands and the Waverley Committee (Waverley, 1954) in England were both commissioned to review what happened and propose a new way forward. Both committees reported a need to establish clear responsibilities for flood defense and initiated discussions as to what was considered an acceptable level of risk. In the Netherlands a national scale benefit-cost analysis was undertaken and used to establish standards for each protective dike ring for the first time (the so-called Delta Plan). The water-related planning processes in the Netherlands were reorganized and clear national and local responsibilities introduced. The first Delta Committee also set out the legal framework for the periodic review and update of the Delta Plan. In 2009, the second Delta Committee was established, and on November 29, 2011, the Delta Act was unanimously accepted in the Dutch Senate including the allocation of €1 billion per year in the Delta Fund (Deltacommissaris, 2011; van Herk, Zevenbergen, Gersonius, Waals, & Kelder, 2015), which strives to balance between investment in protection, prevention, and preparedness while taking into account future change (Gersonius, Ashley, Pathirana, & Zevenbergen, 2010).

1993and1997in Mississippi: Promoted the Need to Acknowledge Uncertainty The 1993 Mississippi River flood was most damaging U.S. flood of the 20th century in economic terms (Galloway, 1995). Following this event, flood risk discussions within the United States began in earnest in 1994 and highlighted the need for a change in approach (e.g., Galloway, 2005). The discussions focused on the uncertainties connected with the hydrology of flood events and how this uncertainty should be handled in studies being conducted by the U.S. Army Corps of Engineers (USACE). In 1996 the USACE issued guidelines for the conduct of the hydrology and related economic aspects of studies that would assess the justification for new flood control projects (USACE, 1996) and lead to the seminal publication by the National Research Council into risk analysis and uncertainty (NRC, 2000). Although these documents recognized the need to extend the analysis to include a range of natural events (including those above the notional design standard of a defense), little was done until after the New Orleans floods in 2005. Despite these advances in thinking, no efforts were made to use risk methodologies to guide flood damage reduction activities in the field. At this point in time, the concept of flood risk management was not widely accepted and, in fact, was questioned by several organizations representing floodplain interests.

Europe,1993,1995,1997,1998, and2000: Reinforced the Demand for a Basin-Wide and Strategic Approach Using a Combination of Structural and Non-Structural Approaches Major floods on the Rhine River in 1993, again on the Rhine in 1995 and 1997, and in the United Kingdom in 1998 and 2000 brought increased attention to the growing challenge of flooding (Kundzewicz, Pińskwar, & Brakenridge, 2013; Marsh & Dale, 2002). As a result there was considerable activity as both academic and governmental organizations struggled to provide solutions to growing flood damages across Europe. In 1996 the European Union (EU) launched a three-year research project River Basin Modelling, Management and Flood Mitigation (RIBAMOD; Samuels, 1999) to, among other things, identify the past difficulties in floodplain management, current best practices, and areas for further research. The RIBAMOD process led to additional activities within the European Community that continued the exploration of new approaches, including risk, to deal with flood challenges. In 2000, the EU issued its Water Framework Directive (WFD) addressing the steps necessary to reduce pollution in European rivers and establish river basin management as the framework for cooperative efforts to accomplish the objectives of the Directive (EC, 2006).

In 2001 the U.K. government commissioned an independent review by the Institution of Civil Engineers (ICE). The review, entitled “Learning to Live with Rivers” (Fleming et al., 2001), specifically criticized the reluctance to use numerical computer models to support decision-making and the inadequate representation of the dynamic effects of land use, catchment processes, and climatic variability. The review also concluded that “only by working with the natural river basin response and providing the necessary storage, attenuation and discharge capacity, can sustainable flood risk management be achieved” and that “floods can only be managed, not prevented, and the community must learn to live with rivers.” The lack of a structural understanding was also recognized, leading to the adoption of the Source-Pathway-Receptor model (DETR, 2000, and its translation to flood management; Sayers et al., 2002) together with the need for a structured hierarchal risk assessment method (Sayers & Meadowcroft, 2005) and an ability to assess flood risk at a national scale to support the national prioritization of investment in flood risk (Gouldby, Sayers, Mulet-Marti, Hassan, & Benwell, 2008; Hall et al., 2003b).

In 2003, the water directors of the European Union noted that “flood protection is never absolute and things can go wrong. The question regularly arises as to what safety is available at what price, and how much of the remaining risk has to be accepted by society. Risk management will be the appropriate method to deal with this challenge” (Water Directors of the European Union, 2003, p. 5). They further found that mitigation and non-structural measures “tend to be potentially more efficient and long-term more sustainable solutions” (Water Directors of the European Union, 2003, p. 2).

In 2004, the European Commission (EC) issued a communication to the Council and the Parliament proposing that Member States and the Commission work together “to develop and implement a coordinated flood prevention, protection and mitigation action programme.” The communication highlighted the need for the development of flood risk management plans for each river basins within the EU and outlined steps necessary to carry out such activity. At the same time, the Commission approved the major research project, FLOODsite (Samuels et al., 2010), to examine, in a five-year program, the physical, environmental, and socio-economic aspects of floods. FLOODsite launched projects throughout Europe to follow-up on the work of RIBAMOD to further advance knowledge in preparation for 21st-century flood challenges and concluded that basin-level flood risk management plans and flood hazard and risk mapping will be supported by models that operate at varying levels of detail with differing data requirements and recognize that public participation and local knowledge as invaluable in the conduct of risk management activities.

In 2006 the Dutch Cabinet initiated a major program of investment to re-engineer the river system and improve the safety of 4 million people in the Dutch delta region. The Spatial Planning Key Decision (SPKD) project became known as the “Room for the River” program and was active from 2006 to 2015 (PKB, 2006; Woorden, 2006), focusing on four rivers: the Rhine, the Meuse, the Waal, and the IJssel. The program sought (and delivered) various schemes to reinstate temporary storage areas, lower and broadened active floodplains, and set back and reinforce dikes at many locations within the Netherlands (Rijkswaterstaat, 2016).

Following additional flood events in Europe during the first decade of the 21st century, the European Parliament and Council issued a directive on the “assessment and management of flood risks” (EC, 2007). The so-called “Floods Directive” established a framework for this assessment and management, with the goal of reducing adverse consequences of flooding to human health, environment, and cultural-economic activity in the European Community. As a first step, the Directive required all Member States to conduct a preliminary flood risk assessment of the river basins within their territories, including the assessment of the potential impacts of climate change. It also directed that Member States prepare flood hazard and flood risk maps and flood risk management plans for their river basins. To support the implementation of the Directive, a Working Group on Floods (Working Group F) was established under the Common Implementation Strategy to enable an exchange of lessons and good practice approaches to implementing the directive.

China1991and1998: A Major Reassessment of Policy and Planning Approaches in Recognition of the Need for a More Efficient and Effective Approach Two thirds of the land area in China is prone to flooding. The economically developed eastern and southern regions, which are most severely threatened by floods, contain around half of the national population, one third of the national cultivated land and produce two thirds of the national industrial and agricultural outputs (Cheng, 2005). Despite increased investment in flood control through this period, flood losses continue to increase (echoing the experience in Europe and the United States). After the major 1991 floods in the Huai River and Taihu Lake and the 1998 flood in the Yangtze River, Songhua River, and Nenjiang River, China began to seek new approaches. The desire of the government to support both economic development and protect the environment promoted a change in philosophy from a primary emphasis on structural flood control to one that had a greater emphasis on emergency planning and preparedness. This also included accepting the need to provide a variable standard of defense depending on need. For example, along major rivers levee system designs started to focus on accommodating the largest flood within the most recent 100 years, whereas for major sea dikes the designs sought to accommodate the worst storms experienced in the past 50 years. In middle- and small-sized rivers flood defense standards focused on smaller “normal” floods (GIWP, 2012).

After the 1998 flood in the Yangtze River, China made strategic adjustments to its approach as the economic, natural, and social impacts of flooding became better understood (Cheng, 2005). The developing Chinese approach now focuses on regulating flooding by employing both structural measures and non-structural measures that include reforming social and economic development to be more resilient to flooding (Cheng, 2006; Sayers et al., 2014; Sun, Zhang, & Cheng, 2012). As part of the shift from flood control to flood risk management, the Chinese government began to promote risk awareness (through a national program of flood hazard mapping) and enhance the socially focused management of flood control areas and has moved away from attempting to eliminate floods totally, recognizing the continued existence of a residual risk (GIWP, 2012). Under this approach, the focus is on protecting people and property and minimizing damage when floods do occur.

Asia,2004, Indian Ocean (Boxing Day) Tsunami: Promoted Better Warning, Emergency Planning, and Spatial Planning as Central to Disaster Risk Reduction An earthquake in the Indian Ocean on December 26, 2004, triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean (Lay et al., 2005), killing around 230,000 people in 14 countries and inundating coastal communities with waves up to 30 m high. Indonesia was the hardest hit, together with Sri Lanka, India, and Thailand. This event provided many lessons, including two most critical lessons for flood managers. The first was “early warning leads to early action.” Given even the shortest of lead times people are able to act to reduce consequences. The effectiveness of the action taken relies on the understanding of the risk and hence the motivation to appropriately prepare. Prior to the Indian tsunami neither early warning systems nor awareness campaigns were in place. The second crucial lesson reflected the loss of critical infrastructure during the event. Hospitals, transportation networks, and community centers were often sited in the most exposed locations and lost at the time when they were most needed. Since 2004, considerable effort has been devoted to developing sophisticated early warning systems (becoming operational in 2006; UNSECO, 2006) and mapping the probability of flooding to inform spatial planning and emergency response decisions. In 2012 the system alerted the Indian islands on Andaman and Nicobar following the Banda Aceh earthquake (8.6 magnitude; Pollitz, Stein Sevilgen, & Bürgmann, 2012), but media reports suggest that a combination of a failure to sound the tsunami warning sirens in Aceh (due to power failure) and congestion of evacuation routes undermined the performance. The success of the warning systems is therefore yet to be fully realized or tested, but it will, inevitably, be in the future.

2005, New Orleans: Promoted Need for Better Understanding of Levee Performance and Wider Acceptance of a Risk Management (Rather than Defense-Based) Approach Hurricane Katrina hit the Gulf Coast of the United States in June 2005. The flooding of New Orleans that followed had devastating consequences, with an estimated 1,464 losing their lives (Jonkman, Maaskant, Boyd, & Levitan, 2009) and economic damages exceeding $150 billion (Burton & Hicks, 2005). The review of lessons that followed was highly critical, highlighting “incompetent engineering and a reliance on a single approach of complete protection from flooding” (Jonkman et al., 2005) and the ability of flood structures to provide reliable protection began to be questioned (e.g., Cigler, 2007). Forensic assessment of the causes of levee failure in New Orleans also brought into sharp focus the limited understanding of the integrity of existing levee systems throughout the United States (and in other countries) and the need for new methods and techniques to better assess their condition. The preliminary analysis into the structural condition of protection measures across the United States that followed Katrina, for example, indicated that many of the tens of thousands of kilometers of levees were in an unsatisfactory condition and that the condition of many more was unknown (Link & Harris, 2007; NCLS, 2009) This experience prompted the now widely repeated phrase “there only two types of levees: those that have failed and those that will fail”; a lesson that early flood managers in Japan had realized over 1,500 years ago, as evidenced by the Yoro Code (the governing rules enacted in 757), stipulated that “A provincial governor and district commissioners must patrol dikes along major rivers, and to order people to repair any damage after harvesting rice in autumn. For dike breach, however, command urgent repair as soon as possible.” It appears that flood management in ancient Japan relied on levee construction and possible levee failure was taken into account (Huang, 2014).

Faced with this situation, the federal government collectively began a rapid move from flood control and damage reduction to flood risk management. In May 2006, the U.S. Army Corps of Engineers and the Federal Emergency Management Agency (FEMA) established a national flood risk management program “to integrate and synchronize the on-going, diverse flood risk management projects, programs and authorities of the … Federal agencies, state organizations and regional and local agencies” (USACE, 2011). As one part of this effort, FEMA added emphasis to its National Flood Insurance Program by increasing its efforts to improve risk identification and communication (NRC, 2013). The significance of the impacts also led to the focus on “resilience” (NRC, 2012a, 2012b), a concept that continues to evolve today.

Hurricane Katrina also led to a reassessment of the organizational structures in the United States. The long-standing federal leadership of flood control and flood damage reduction activities within the United States was revisited, and the federal organizations identified that flood risk management should be the joint responsibility of all levels of government and those who live, work, or influence activity in flood risk areas. They also emphasized that flood risk management not only will require consideration of structural measures to deal with ongoing and future risks but will also involve full use of available non-structural techniques (Link & Harris, 2007). Figure 2 illustrates the multi-faceted approach to “buying down” flood risk that emerged from these discussions, an approach that echoed the concepts of a “portfolio-based approach” promoted in the aftermath of the 2000 floods in England (Evans et al., 2004a, 2004b) and the Multi-Layer Safety Approach promoted in the Netherlands (VenW, 2009).

Figure 2.(left) The risk reduction concept as applied to the FloodSAFE program of the state of California (courtesy of California Department of Water Resources) (right) Multi-Layer Safety Approach (Netherlands).

2007 Floods in Hull, UK: Promoted the Need to Consider All Sources of Flooding and Spatial Coherence of Events Following a major flood in 2007, the British government commissioned Sir Michael Pitt (the Pitt Review; Cabinet Office, 2007) to review the lessons learned from this event. The subsequent report to the government discussed both technical and organizational shortcomings. It also identified that having a legislative framework for flood risk management was fundamental, noting that “the management of flood risk requires concerted action by public and private bodies, and this must be properly supported by appropriate legislation that would address all forms of flooding.” This was an important lesson highlighting that floods are generated by many mechanisms, and an understanding of each is required to manage flood risk effectively. Until then, coastal and fluvial (river) flooding had been the responsibility of one organization and groundwater, and perhaps more importantly, pluvial (direct rainfall) flooding another. The Pitt Review also led directly to the development of surface water management plans in the United Kingdom, a layer of planning where all sources of flooding are considered and an attempt is made to develop integrated management strategies.

UK2013/2014and2015/2016Floods: Led to the Recognition that “The Design Storm Is Dead” and Re-Emphasized the Importance of Natural Flood Management Despite the general move toward a “risk-based approach,” the widespread floods across the United Kingdom in 2013/14 and 2015/16 highlighted continued failing. In response to the 2015/16 flood two major reviews were undertaken: the National Flood Resilience Review (HM Government, 2016) and the Environment Food and Rural Affairs committee report (EFRA, 2016). These reinforced the need to consider flooding from multiple sources (pluvial, fluvial, coastal, groundwater) to underline the importance of nature-based responses and the need to use improved numerical forecasts and catchment scale models to support decisions (echoing a similar call from 2001) and to understand the escalation of impacts that can result from loss of important municipal infrastructure (e.g., the Resilience Review found 530 important infrastructure sites, such as water and telecoms, were exposed to a significant chance of flooding, with each potentially affecting at least 10,000 people). Each review contained many recommendations covering the need for more integrated modeling and planning (echoing pervious reviews). The most significant new insight, perhaps, focused on the need to better understand and prepare for storm sequences. This issue was brought into sharp focus when a seafront railway line in Dawlish, Devon, collapsed when exposed to repeat, but moderate, storms that lowered the beach, allowing large waves during subsequent storms to impact the line (Shaw, Dawson, & Gehrels, 2016). These events highlighted that the performance of flood infrastructure (both green, grey, hybrid) is sensitive to the temporal clustering and sequencing of storms and exposed the inadequacies of traditional flood defense design approaches based on a single design storm, leading to the recognition that the “design storm is dead” (Sayers, Walsh, & Dawson, 2015b) along with the assumption of climate stationarity (Milly et al., 2008).

A summary of these events, together with other pivotal floods over the past century, is given in Table 1.

Table 1. The Influence of 20th- and 21st-Century Flood Events in Shaping Policy and Practice.

Flood Event

Impact on Thinking, Policy, and/or Practice

1917 Mississippi River and the Sacramento River basins, US, and 1927 lower Mississippi, US

Promoted the need for basin scale infrastructure and coordination

1931 and the following decades, across three major rivers: the Yellow, Yangtze, and Huai, China

Promoted the need for basin scale infrastructure and coordination

Major floods across the United States in 1936 (and to a lesser extent 1937 and 1951)

Reinforced the need for national responsibility

In March 1947, river floods occurred across much of Europe, Shortly after Europe experienced devastating coastal floods in 1953

Issues of food security, the need for clear roles and responsibilities, and the performance of warning systems

1991 and 1998 China

A rethinking of flood issues: how to carry out disaster mitigation approaches more efficiently and effectively

1993 and 1997 Mississippi, US

The 1993 Mississippi River flood was the U.S. flood of the century in economic terms; following this event, new regulations were issued (1996) that established the need to include uncertainty in the assessment and justification for new flood control projects

1993, 1995, 1997 on the Rhine and 1998 and 2000 in the UK

Led to a demand for a new basin wide and strategic approach to flood management using a combination of structural and non-structural approaches

2004, Asia Tsunami (Boxing Day)

A recognition of the vulnerability of coastal communities and need for better warning, emergency planning and spatial planning to reduce risk

2005, New Orleans, US

A wider recognition that levees fail; a need to better understand levee performance and the wide acceptance of the need for a risk management approach and the communication of residual risks

2007, Hull, UK

The need to consider all sources of flooding and spatial extent of events, as pluvial, fluvial, and tidal sources combine

2013/4 and 2015/16 across England

The need to reevaluate the approach to the assessment of risk use of floodplains, limitations of structural systems, and the need for improved resilience of critical infrastructure and prevent secondary and tertiary risks developing

Despite remarkable progress, good flood management is a complex endeavor, and many management challenges persist.

How to Deliver Appropriate Integration?

Despite multiple initiatives to promote an integrated approach to flood risk management (Samuels et al., 2010; WMO, 2009), progress has been slow. In general, this is because in a complex reality truly integrated solutions are often consumed by protracted debates and remain trapped in an endless process of planning and discussion. Equally, decision-making rooted in sectoral silos offers an overly narrow functional focus and prevents the horizontal and vertical integration required as collaboration and integration can be perceived as either inconvenient, threatening to existing functional relationships, or as an added burden.

An appropriately integrated approach is needed, one that leads to long-term solutions. This requires a step change in the way urban and rural development needs are delivered while safeguarding and promoting natural capital. Such an approach would allow a broader range of trade-offs to feature in the discussion and enable innovative solutions to be co-developed, co-funded, and implemented. In addition to appropriately designing and maintaining flood defenses and continuing to improve warning systems, this will increasingly include paying landowners to add temporary upstream storage, encouraging spatial planners to actively reduce risk (not just avoid increasing it), and ensuring the most vulnerable can access affordable insurance and property level grants. Small-scale case studies and pilots are emerging in support of this view, but these need to be upscaled and mainstreamed.

Challenges also remit in “joining up” national, regional, and local governments to ensure multiple policies, regulations, and programs they promote are appropriately integrated and that work done at one level of government, or in one sector, is in harmony with associated activities in other levels of government and sectors. As such “sound” flood management planning requires a paradigm of governance that is collaborative and blurs the distinction between the disciplines of spatial, coastal zone, river basin, and water resources planning as well as flood defense engineering and environmental management. This is not easy, and achieving meaningful horizontal integration is a significant challenge, requiring flood managers that are used to working within “regulatory instruments along vertical paths of the administrative hierarchy” to “cultivate more intensively forms of horizontal integration” (Moss, 2004, p. 90). Despite the management of flood risk being seen as part of the wider process of water management, flood management practice still often fails to deliver integrated solutions.

How to Deliver Innovative, Long-Term Solutions?

As set out by the Chief Scientist in 2015 (Penning-Rowsell, Sayers, & Watkinson, 2014), to be successful a society must learn to manage risk and not simply seek to avoid it—a philosophical and practical impossibility in the context of flood risk. Innovative solutions, and how to generate the political momentum to deliver them, remains a central barrier to progress. For example, the policy in recent years within England and Wales has been guided by the principle of “Making Space for Water” (Defra, 2005) and, in the Netherlands, “Room for the River” (Ministry of Infrastructure and the Environment, 2006). The sentiment of these policy goals is clear but often at odds with the local political and public response to a flood event (e.g., for better protection from flooding), local economic development choices (e.g., with continued development in the floodplain, for example), and insurance industry agreements that focus on reducing the chance of flooding. Only where it is easy to “make space/room” is this done. Experience in practice reinforces strategic flood management as a human endeavor and one that requires clear leadership and collaboration to be successful.

How to Secure Whole-Life Financing?

Many well-intentioned plans have failed due to the lack of clear roles and responsibilities (with associated budgetary security) that bridge the gap across policy, planning, and implementation (Sayers et al., 2013). In particular, the funding of maintenance has been an Achilles heel of a more strategic approach. Far more effort is typically placed in the initial construction of such facilities than is devoted to routine maintenance, periodic upgrades, and ultimate removal/replacement. Without adequate resources, new infrastructure can rapidly deteriorate and fail to provide the level of performance they were designed to provide, undermining an entire plan. Whole life costing is now widely promoted as an analysis tool but typically not allied to a long-term funding commitment. This is the case for both major investments (in England, for example, the Environment Agency agreed to a six-year expenditure settlement with central government on a rolling national program; Environment Agency, 2015) and more local community-based responses (for example, questions over the funding for long-term maintenance of sustainable urban drainage, temporary and demountable defenses continue to slow uptake in practice, e.g., Geaves & Penning-Rowsell, 2016).

How to Embed Effective Participation in Decision-Making?

Implementing a more strategic approach to flood risk management places a high demand upon its stakeholders. It involves the collective action of a range of different government authorities and those outside government, including the public and business. This places an increasing emphasis upon effective communication and mechanisms to reach consensus without succumbing to the short-term thinking that may be present within the many competing views. Increasingly, the move toward flood risk management is becoming embedded in national government policy. This includes, for example, Making Space for Water in the United Kingdom (Defra, 2005), the European Directive on the Assessment and Management of Flood Risks (EC, 2007), and progressive evolution of floodplain management in the United States (Galloway, 2005; IFMRC, 1994; Kahan et al., 2006).

Until late in the 20th century, little was done to involve those living in the floodplain other than farmers in the development of flood mitigation activities. Public participation is now universally considered to be an essential element of flood risk management and will take an increasing role. Attention is being focused in Europe and the United States on use of advanced public involvement techniques such as Shared Vision Planning and similar approaches that bring the public into the decision process in a collaborative manner. China has successfully worked to organize the army and civil society to manage flooding on a scale largely unseen elsewhere. Ownership over local ecosystem rehabilitation and construction activities is starting to emerge, such as returning farmland to forests, planting trees, and conserving soil and water to restore original ecological features, together with the engagement of the public in monitoring the condition of river channels and dikes.

The next decades, with the availability of information through multiple media and the ability of decision-makers to access big data analytics, will see an increase in demand for, and ability to support, participatory decision-making (not only during emergencies, the focus of the majority of current efforts (e.g., Conrado, Neville, Woodworth, & O’Riordan, 2016), but increasingly in support of longer term management). Flood professionals must develop methods to better communicate their message and engage the public in the new risk management processes and secure their active participation in planning efforts—both locally and nationally to ensure support for what are likely to be significantly increased resource expenditures.

How to Reduce Impacts While Maximizing Multi-Diverse Opportunities?

Many rivers were managed during the 19th and 20th centuries with single purposes—navigation/trade, flood control, hydropower, water supply, etc. There is today, and will be in the future, increasing emphasis on promoting multipurpose use. Managing rivers and coasts therefore presents both opportunities and challenges for joint uses and multiple benefits. Flood storage behind the reservoir could, for example, be traded for hydropower production to create a fiscal profit pool that could be used in turn to compensate those in the floodplain for damages. Trading navigation storage for hydropower or water supply in some reaches could be balanced against navigation operations in other reaches. How best to combine these demands in an effective and practical way will be an enduring challenge demanding much stronger strategic basin planning. Within this context, perhaps two of the most pressing challenges are:

•How to deliver environmental benefits alongside flood management: Many rivers and coasts in the developed world are now cleaner than they have been for many years, and efforts to improve ecosystem health continue. For example, multibillion-dollar restoration projects are underway in many places including the Danube River in Europe and the Florida Everglades in the United States, and many other restoration projects are planned (on large and small scales). The challenge now is to build upon these efforts and examine how restoration projects could be used not only to bring back endangered ecosystems but also to serve as valuable adjuncts to flood risk management efforts.

•How to combine climate adaptation and mitigation: As the world begins to accept the necessity of dealing with climate change, there will be increased pressure to reduce national carbon footprints. Floodplains have been cited as ideal locations for crops that can be used for carbon sequestration. Experiments are taking place around the globe to determine physically, economically, and fiscally how such programs might be developed. Use of existing and restored wetlands may become extremely important in carbon banking scenarios. Little has been studied to appreciate both the positive and negative aspects of this use of floodplain areas and the impact it might have on flood risk management activities.

How to Develop Flood Strategies that Address Local Issues as Well as those of the Larger Watershed?

The need for planning on a basin scale to avoid upstream–downstream conflicts is now well recognized within the flood risk management community. Its uptake and impact on broader planning processes and behavior is less clear. Going forward, ensuring that flood risk plans are carefully coordinated with other functional activities such as land use, industrial development, and national intentions will be a significant and important challenge. This challenge is made harder because governments and businesses have always been most comfortable operating within an organizational structure that permits activities to be carried out that relate to their narrow field of interest. Although it is now widely accepted that flood management must be addressed at the whole river basin or coastal cell level, or even the entire country, such efforts require considerable collaboration. Changing these perceptions will remain a significant practical challenge going forward, and initiatives such as the EU Water Framework and Flood Assessment and Management directives and the appointment of a catchment director in the aftermath of the 2015/16 floods in Cumbria are welcome support to making progress in this area basin-level planning and cooperative (e.g., Gibbs, 2016; Samuels et al., 2010).

Strategic Flood Risk Management

What Is Strategic Flood Risk Management?

Supporting sustainability through a strategic approach to flood management is much more than simply maintaining the long-term integrity of flood control structures—a common misconception in many parts of the world. It also includes promoting the long-term health of the associated ecosystems, societies, and economies. In recognition of this, a common understanding of what constitutes SFRM is now starting to emerge that builds upon the general concepts of risk and has been defined as follows (Sayers et al., 2014, p. 2.):

The process of data and information gathering, risk analysis and evaluation, appraisal of options, and making, implementing, and reviewing decisions to reduce, control, accept, or redistribute flood risks. It is a continuous process of analysis, adjustment and adaptation of policies and actions taken to reduce flood risk (including modifying the probability of flooding and its severity as well as the vulnerability and resilience of the receptors threatened). Strategic Flood Management (SFM) takes place as part of a wider approach of integrated basin or coastal planning and focuses on reducing flood risks and promoting environmental, societal and economic opportunities (both now and in the longer term). It recognizes that risks can never be removed entirely and that reducing risk is often at the expense of other societal goals.

This definition contrasts with the linear management model, based upon set standards and a more certain view of the future, that is characteristic of traditional flood control decisions. It urges flood managers to recognize that future conditions may change (perhaps significantly) from those that exist today and seeks to embed resilience and adaptive capacity within the choices made and to adopt a continuous process of monitoring and intervention (Sayers, Galloway, & Hall, 2012; Willows & Connell, 2003). To translate this definition into practice, a small number of “golden rules” of SFRM have emerged. These are discussed in detail in Sayers et al. (2014) and summarized in Figure 3.

What Progress Has Been Made to Date?

Understanding the shortcomings of traditional flood defense or flood control paradigms is not enough to change practice. This can be readily observed through the continued focus upon reducing the probability of flooding through extensive structural defense systems (such as those in Rotterdam, New Orleans, and on the Huai River in China). To make a step change in the incremental process of evolution is now the challenge. Although there is no single roadmap to aid this transition, and few comprehensive examples, many elements of good practice are starting to emerge. For example, non-structural measures are increasingly recognized as vital components of a broadly based approach to managing risk, and various documents now reflect this direction of travel in modern flood risk management, including:

• Spatial planning that makes space for water (as embedded in the “Room for the River” policies in the Netherlands and “Making Space for Water” in England; Defra, 2005) and controls the number and type of new developments in flood prone areas (e.g., Barker & Coutts, 2016; Burby & Dalton, 1994; see also various national and local planning guides).

• Dual-purpose buildings that provide a safe haven and a community facility such as a school or clinic (see, for example, the Bangladesh Flood Action Plan) and multi-purpose flood infrastructure that contributes positively to the urban setting, providing amenity and ecosystem services in periods between floods, e.g., Maksimović, Stanković, Xi, & Lalić, 2013).

• Awareness of the risks faced to enhance preparedness through the provision of readily accessible information on all sources of flooding, including national flood mapping (e.g., Environment Agency, 2010a).

How Can SFRM Support the Broader Aims of Sustainable Development?

The overarching motivation for flood management is to support the broader aims of sustainable development (UN, 1992; WCED, 1987), a central consideration that underpins the Hyogo Framework for Action (ISDR, 2005), the Sendai Framework for Disaster Risk Reduction (UN, 2015), and many of the Sustainable Development Goals (UNDP, 2016). SFRM can play a pivotal position in promoting desired societal, environmental, and economic outcomes. As such, and in contrast to the often narrowly defined single objective nature of flood control paradigm, strategic flood management places an emphasis not only on reducing risk (to people, economics, and the environment) but also on seeking opportunities to work with natural processes and promote multiple benefits across a range of criteria (ecological, societal, and economic). The trade-off between the resources required and benefits accrued lies at the heart of investing limited resources effectively and efficiently. In particular, the way in which the social justice, adaptation, and ecosystem services are addressed through flood risk management planning and policy is, as discussed in the following section, crucial.

Delivering Social Justice

Flooding, and actions taken to manage floods, are not fair per se due to the inherent natural spatial inequality in the frequency and extent of flooding, plus the legacy of past interventions and the coverage of new ones. What is “fair” in the context of flood management therefore reflects a broader notion of social justice and the approach taken to managing risk and prioritizing investment in risk management actions (Johnson et al., 2007; Penning-Rowsell, Priest, & King, 2016). A socially just approach to flood risk management decision-making therefore aims to maximize the return on investment while ensuring that investment is distributed through an equitable process and see that the most vulnerable members of society are protected. This aim can be considered more formally in the context of three social justice models (Rawls, 1971): (i) an egalitarian approach (where all those at risk are treated equally); (ii) a utilitarian approach (fair to those that fund but not necessarily benefit from action; in England, for example, the public taxpayers provide the majority of funding for flood risk management and typically advocate some form of benefit cost test to determine worthwhileness and the efficiency of investment in particular action), and (iii) the Rawlsian “maximin” rule that proposes “positive discrimination” in favor of the most vulnerable (Table 2). These models of social justice have been explored in a number of projects (see Nada-Rajah, 2010) and recognized as part of “good” SFRM (Sayers et al., 2014). Achieving socially just outcomes continues to be difficult to achieve in practice (Kazmierczak, Cavan, Connelly, & Lindley, 2015; Lindley et al., 2011; Sayers et al., 2016b). In part this may be a considerable challenge given that the achievement of one form of equality tends to preclude the achievement of another form of equality (Sen, 1986), but acknowledging that risk cannot be managed simply on the basis of calculations of probabilities multiplied by unwanted outcomes and the balancing of costs and benefits is an important first step. Doing so places social justice at the heart of the choices made and can help focus attention on deciding “what is the right thing” (Vojinović & Abbott, 2012).

Every citizen should have an equal opportunity to have their flood risk managed.

In some countries, such as the Netherlands, the principle of “solidarity” seeks to provide a common minimum level of protection to all individuals (e.g., van Alphen, 2014).

The heterogeneity of the flood risk in England, however, means that such an approach, even if achievable would be grossly inefficient (Defra, 2004). Instead, a consistent decision process is sought that gives those at risk from flood a fair chance of receiving tax funded investment.

Discriminatory (distributive and procedural)

Rawls’s “Maximin rule” that seeks to direct resources to those least able to help themselves

Options are chosen that target the most flood vulnerable members of society (even when greater economic returns can be found elsewhere)

The most vulnerable individuals and communities need to be identified and plans developed that specifically cater for their needs.

Policy and planning processes to incorporate bias to ensure preference is given to managing flood risk for most vulnerable individuals and communities. Although many policy goals promote preferential targeting of the most vulnerable, the only tangible expression of this (known to the authors) within the decision-making process is in England’s Flood Defence Grant-in-Aid scheme.

Utilitarian (distributive and procedural)

The return on investment is maximized to ensure the greatest risk reduction per unit of resource input

Assistance provided to those members of society to which the benefits offer the greatest gain to society

A prioritized program of investments that provides the greatest return (reduction of risk) for each unit of resource. Acting in priority of return on investment.

The adaptation of a common approach to the assessment of benefits and costs and the analysis of benefits and costs to identify those actions the yield the greatest return (e.g., Environment Agency, 2010b). Increasingly this process reflects whole-life costs and the multi-benefits under multiple futures (although readily monetized benefits continue to dominate this process and potentially undermine the ability to maximize utility).

Safeguarding and Promoting Ecosystem Services

Ecosystems provide critical provisioning, regulating, and cultural services (UN, 2005). Without early consideration of how best to safeguard and promote, these flood management choices can have a devastating impact (e.g., as experienced in the Danube basin leading to significant restoration needs). “Soft path” measures (such as land use changes, wetland storage, and floodplain reconnection) and selective “hard path” measures (such as bypass channels or controlled storage) offer opportunities to simultaneously manage risk and promote ecosystem services (Opperman, Galloway, & Duvail, 2013; Sayers et al., 2014).

Until very recently, although always appreciated at a local scale and in academic terms, little attention was given to maintaining the beneficial relationship between floods and ecosystem services in actual flood management planning. For example, in near-complete ignorance of the ecological value of wetlands, during the middle of the 19th century, the U.S. Congress passed legislation that supported the draining of wetland areas to provide room for agriculture and provided funding for flood control activities (e.g., The Swamp and Overflowed Lands Act of 1850 ensured that the state would be responsible for funding the attempts at developing wetlands into farmlands; Dovell, 1948). The Congress saw little value in these periodically inundated areas. The lack of understanding of the natural and beneficial functions of floodplains inherent in this legislation set the tone for the treatment of the floodplain environment that would continue in the United States over the next century and reflected practice across much of the Western world at that time (as testified by the infrastructure systems that remain, from the hidden rivers of London (Talling, 2011) to the concrete lined trapezoidal channels characteristic of many urban storm channels in the United States and elsewhere).

To make gains in safeguarding and promoting ecosystems through flood management, a shift in emphasis is required. Working with natural processes needs to become a much more central consideration—a requirement acknowledged, for example, with the recent initiative of the Environment Agency in England to promote the concepts of working with natural processes in flood risk management (Environment Agency, 2012) and the recent adoption of “natural flood risk management” into Scottish legislation (SEPA, 2012). Implementing natural flood management presents many practical, as well as policy, challenges. Settlement and development in the floodplain continues today with many of the world’s most dynamic cities located in river deltas and estuaries (Bangkok, Shanghai, New York, London, New Orleans, and many others). This places more and more people and property in harm’s way, and, as in the past, structural measures continue to dominate (see, for example, the development of major levee and sluice systems within the Taihu Basin, China (Xie, Sayers, Sun, & Zhang, 2012) or the “Stormwater Management And Road Tunnel” or “SMART Tunnel” in Kuala Lumpur, Malaysia). In many developing countries the reliance upon structural measures reflects the nature of the significant flood issues faced but also national policies that remain based on flood fighting and control rather than flood management. Elsewhere, continued development in the floodplain and reliance on single-purpose structural measures appears to reflect a lack of imagination (in funding and design) rather than constraints within policy.

Good practice is, however, emerging. In California the Delta Stewardship Council, created in legislation under the Delta Reform Act (2009), is mandated by the state to achieve so-called “coequal goals” for the Delta with the aim of “providing a more reliable water supply for California and protecting, restoring, and enhancing the Delta ecosystem. The coequal goals shall be achieved in a manner that protects and enhances the unique cultural, recreational, natural resource, and agricultural values of the Delta as an evolving place.” (CA Water Code §85054). Improving flood protection by structural and nonstructural means is planned in the context of this broader framework (Delta Stewardship Council, 2013).

Ensuring Resilience

The notion of “resilience” has been a common framing within ecosystem and human health literature for many decades but did not enter the U.K. “risk” policy arena until the publication of the Civil Contingencies Act (2004) and the setting up of Local Resilience Fora. Flood resilience was not specifically considered until the publication of the Pitt Review (Cabinet Office, 2007) that followed the widespread flooding experienced in 2007 and the subsequent Strategic National Framework on Community Resilience (Cabinet Office, 2013). In parallel “flood resilience” was also moving center stage international and came to prominence following the devastating impacts of Hurricane Katrina in 2005 and the publication of the Hyogo Framework (ISDR, 2005).

Despite these advances, as yet no blueprint is available as to what constitutes resilience in a practical sense. There is, however, an emerging consensus on the four characteristics that a resilient community may exhibit (e.g., Sayers et al., 2012; Twigger-Ross et al., 2014), namely:

•Resist: an ability to resist (i.e., for flood defense to remain structurally intact or a warning service to continue to operate) when exposed to a wide range of threats, including ones that are not necessarily foreseen during the planning or design process. Equally, “resistance” implies an ability to fail incrementally and not catastrophically when subject to hazard events more severe than those planned for. It also implies a degree of redundancy in the system that prevents risks from cascading (from a primary source to a secondary source or through the supply chains) and hence may help avoid an escalation of risk—through communities, regions, national, and even global economies (Rinaldi, Peerenboom, & Kelly, 2001). The notion of interdependent infrastructure systems and how the critical services they provide (water, energy, transport, etc.) could be affected by spatially coherent flood events has been an increasing focus of research since the Asian tsunami, 2004. The system of system approaches (Hall, Henriques, Hickford, & Nicholls, 2013) provides useful insights into critical odes within complex systems and how they can be restructured to better “resist” flood events.

•Recover(bounce-back): an ability of the human or ecosystem to recover rapidly from a flood event with limited emergency aid in a way that supports a rapid return to normality. Measures that are in place prior to the flood to aid recover from an event, such as insurance and emergency service provisions, can significantly improvement recover times and make a legitimate contribution to “resilience.”

•Adapt (adjusting to a new normal): an ability to modify existing approaches (physical defenses, organization’s structures, behavior, etc.) in recognition of a changing situation. Adaptation, in context, refers to the ability to enact a process of ongoing moderate change in approach.

•Transform (step change): having the foresight and ability to change radical changes in risks and opportunities (physical, social, ecological, economic) that may occur in the future in a timely and equitable manner.

The first two characteristics support the notion of “reactive resilience” where the approach to the future is to maintain the status quo and the quest is for constancy and stability (Dovers & Handmer, 1992). The last characteristics support the notion of “proactive resilience” and the acceptance that change is an inevitability and a resilient system is one that is capable of the necessary change (Dovers & Handmer, 1992).

Achieving these characteristics challenges traditional flood risk management practice. In particular, a new approach to assessment, planning, and implementation is more strategic in nature and based upon:

A whole system understanding: Many authors (e.g., Cutter, 2010; ENSURE, 2009; Liao, 2012; Newman, Ashley, Molyneux-Hodgson, & Cashman, 2011) note the change in concept from an engineering, structural concept of resistance (an ability to withstand loads that are greater than design) to the more interdisciplinary concept developing system resilience. The understanding of “whole system” is increasingly used to describe the coupled human–ecological system that brings together the physical system (e.g., the sources, pathways, and receptors of risk (Sayers et al., 2002) with organizations, communities, and individuals that influence the behavior of that system in the short and longer term). In particular, this involves developing an understanding of flood risk, vulnerability, and uncertainties and using each in support of good decision-making (Figure 4).

Figure 4. An understanding of vulnerability, risk, and uncertainty is needed to make informed choices (Sayers et al., 2016).

A whole-system, portfolio-based, response: Strategies based upon a wide portfolio of structural and non-structural responses typically offer a degree of redundancy that promotes greater resilience than relying upon a single measure. Strategies consisting of individual response and structural measures, however, will continue to remain a legitimate component in all but the lowest of risk areas (e.g., Evans et al., 2004a, 2004b). “Resilient design” fosters an innovative approach to the design, construction, and operation of these (Bosher, Carrillo, Dainty, Glass, & Price, 2007; NIBS, 2010). This can help ensure that an acceptable level of performance is maintained when exposed to events more severe than anticipated (i.e., levees should not breach when a notional design level has been exceeded, nor should their performance decay catastrophically without warning).

The ability to recover failed infrastructure rapidly is vital in supporting the timely return to normality. This can be supported by good design choices that avoid the need for complex planning, highly specialized skills, or difficult-to-source materials when making a repair.

A prerequisite to avoid the rapid escalation in the severity of a flood event is to ensure that critical infrastructure (e.g., energy, transport, communications, and emergency services) continues to function (a central lesson from the Asian tsunami, as impacts escalated as they cascaded through global supply chains; see Table 1). Identifying critical components within these networks relies on an understanding of the independencies that exist within and across sectors, an understanding that is rapidly developing (e.g., Hall et al., 2013) but will demand coordinated action to mainstream into practice.

Implementation through a continuous process of adjustment: Developing and implementing adaptive strategies relies upon creativity and innovation in (i) selecting responses that do not foreclose future options or unnecessarily constrain future choice, (ii) using responses that are effective under the widest set of plausible future scenarios, (iii) observing change through targeted monitoring and continuing reassessment of scenarios of the future, and (iv) appropriately modifying policies, strategies, and structure plans. Maintaining future flexibility (to either raise a defense or make a significant change in approach, such as abandon a town) is not, however, a zero-cost option and will often add to upfront costs (e.g., to strengthen foundations in preparation for future crest raising). Deciding how much to invest in future flexibility can be difficult, but structured, and practical, approaches are now emerging to support decision-makers in accounting for adaptive capacity in options appraisals in a way that credibly takes account of future uncertainties (e.g., Brisley et al., 2015; Haasnoot, Kwakkel, Walker, & ter Maat, 2013; Walsh et al., 2013). Adaptive approaches are also appearing in real-world strategies, including, for example, the development of a long-term flood risk management plan for the Thames Estuary through London (Thames Estuary 2100, or TE2100) that offers an early example of an adaptive strategy. TE2100 expresses possible actions as a function of sea level rise (ranging from 0 m to 4 m) in the form of a decision tree. Progress through the decision tree is conditional on sea level rise (as it becomes better known) and any preceding decisions made (McGahey & Sayers, 2008; Tarrant & Sayers, 2012). The characteristics that make a potential flood management option more or less inherently flexible and adaptive are also starting to be recognized (Sayers et al., 2015b). Inherently more flexible options are, for example, likely to favor reducing vulnerability in preference to providing protection, making space for water, and delivering multiple benefits (Figure 5).

Throughout history, flood management practice has evolved in response to flood events. This heuristic approach has yielded some important incremental shifts in both policy and planning (from the need to plan at a catchment scale to the recognition that flooding arises from multiple sources and defenses, no matter how reliable, fail). Progress, however, has been painfully slow and sporadic. A new, more strategic, approach is now needed.

Strategic flood risk management (as set out in this article) offers a practical policy and planning framework to transform the understanding of risk and move toward a flood-resilient society. A strategic approach to flood management involves much more than simply reducing the chance of damage through the provision of “strong” structures and recognizes adaptive management as much more than simply “wait and see.” SFRM is inherently risk based and seeks to actively manage future uncertainty, a characteristic that sets it apart from the linear flood defense planning paradigm based upon a more certain view of the future.

This article has set out how SFRM adopts a broad view of the present and future risks to, and opportunities for, social well-being, the economy (local and national), and ecosystem health. It explicitly considers the whole flood system and promotes a portfolio of policies and measures to be implemented through a continuous process of review and adaptation. In doing so, SFRM accepts that there is no silver bullet for flood issues and that people and economies cannot always be protected from flooding. It accepts flooding as an important ecosystem function and a legitimate ecosystem service is its contribution to flood risk management. Perhaps most importantly, however, SFRM enables the inherent conflicts as well as opportunities that characterize flood management choices to be openly debated, priorities to be set, and difficult investment choices to be made.

Acknowledgments

The opportunity to submit this article to the Oxford Research Encyclopedia of Natural Hazard Science is gratefully acknowledged. The research underpinning this article has been funded by a number of organizations, most notably WWF as part of their ongoing collaboration with the General Institute of Water Resources and Hydropower Planning, China, focused on strategic water management and the NERC FORUM Grant (NE/M008851/1) led by the Environmental Change Institute, University of Oxford.

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